i was hoping someone had some ideas as to why my two ecobee switches might turn on the light in the rooms where they are located when my ac turns on with no occupancy. I have been over this with ecobee numerous times already and have gotten no where. they tell me there is no correlation between my ac thermostat which is an ecobee 3 and the ecobee switches yet without a doubt with the smart on features enabled on my ecobee switches when the ac turns on (fan specifically) the light will come on in the room close to the thermostat almost every time and sometimes in the master bathroom where the other is located. now when I disable the smart on features on the switches this 100% does not happen. I removed all my ecobee products from smart things and it still does it, I covered the vent thinking the cool air was triggering occupancy but it still does it, even covered the sensor. I even replaced the light in the one room with an led light and it still does it. I’ve also turned off the wifi because all these devices are on the same wifi thinking the ecobee 3 was sending some command to the switches but it still does it. so i’m down to the wiring in my house, I should mention when the ac comes on the light in the living room flickers slightly, its a somewhat older house, early 90’s. anyone have an ideas what could trigger occupancy for those switches, like I said the light comes on the exact moment the fan comes on and sometimes off, but only when the smart on features are enabled. could it be something with the wiring in the house? thanks

Are we talking central air? Where is the vent in relation to the switch? The switch is most likely detecting a change in the temp in the room and thinking it’s a person. PIR motion sensors respond to heat/cold.

Does the cold air come up right behind the switch in the wall? The only thing to do to truly eliminate the switch placement in relation to your ac is to move the switch. When your AC comes on does the switch turn on immediately or does it take a second or two?

the vent is above the switch on the ceiling about 2 feet from the wall where the switch is but aligned with it directly. the light will come on not exactly when the ac comes but exactly when the fan kicks on which is a few seconds after the ac. I should also mention this is the second ecobee switch that ecobee sent me, the third new one is in the master bathroom, it will do it on occasion.

Sounds like @Ryan780 nailed it: simple PIR sensors, such as those in the ecobee switch, work by detecting very small variations in heat passing across the sensor. It’s classic that these will come on when an air conditioner comes on.

The only reason I’m posting is to explain why you probably didn’t have this problem with your Lutron devices. Lutron is an engineering company focused on lighting with literally hundreds of patents on various kinds of lighting technology, including occupancy sensors. Although they do use PIR sensors, they combined them with other kinds of sensing in order to reduce exactly these kinds of false alerts.

So it wouldn’t surprise me at all that you didn’t have the problem with Lutron devices and you did with the new ecobee switches.

I know that doesn’t help your current situation, but I just thought some people might wonder why there was a difference when you switched brands.

I appreciate that, I was thinking ecobee could use some Lutron “advisors”. I wouldn’t want to put something like that out there if it were that unreliable but odds are this will not happen to most. makes me wonder about https://idevicesinc.com/evolution/ which I was considering as well. I like the idea of alexa in a switch in places like a small room or bathroom, kitchen even, without having to get another echo device.